Django has multiple databases and each database has its own group of applications

Question

I have a group of Django applications need to be placed in its own Postgres database instance

Let say I have app1, app2, app3, app4, app5, app6. And I have multiple database instances for them

DATABASES = {
    "default": env.db("DATABASE_URL", default="postgres://postgres:postgres@localhost:5432/th_life"),
    "analytic": env.db("ANALYTIC_URL", default="postgres://postgres:postgres@localhost:5432/th_life_analytic"),
    "product": env.db("PRODUCT_URL", default="postgres://postgres:postgres@localhost:5432/th_life_product"),
    "customer": env.db("CUSTOMER_URL", default="postgres://postgres:postgres@localhost:5432/th_life_customer"),
}

For sake of simplicity I will give an short example default and customer I need app1, app2, and app3 go to customer database instance

class DBRouter(object):

    def __init__(self):
        print(f"Customize router")
        super().__init__()

    def db_for_read(self, model, **hints):
        # customer information
        if model._meta.app_label in ['app1', 'app2', 'app3']:
            return 'customer'
        return None

    def db_for_write(self, model, **hints):
        if model._meta.app_label in ['app1', 'app2', 'app3']:
            return 'customer'
        return None

    def allow_relation(self, obj1, obj2, **hints):
        if obj1._meta.app_label in ['app1', 'app2', 'app3'] or \
            obj2._meta.app_label in ['app1', 'app2', 'app3']:
            return True
        return None

    def allow_migrate(self, db, app_label, model_name=None, **hints):
        if app_label in ['app1', 'app2', 'app3']:
            return db == 'customer'
        return None

After I tried migrate app1. It is not apply schema to the target database. It goes to default database instance

Question:
What is the correct way to group my applications to particular database instance?

References:
I had tried some of them and many of them are outdated or no answers

Official docs

multiple databases and multiple models in django

Django Database router based on user selection

django database routing with transactions

Dynamic database routing in Django

Django migrations router databases

Django database router

Different database for each django site

Configure Django Database Routers